Am Freitag, 5. September 2008 09:06 schrieb Bart Massey:
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I think it would be better to expand the definition of of groupBy such that the equality test is applied only to adjacent elements (with the arguments in proper order). This would not change the behavior for true equality predicates, but would permit cases like incp to have sensible behavior, which can occasionally be useful. (It was to me in this case: I was identifying straights in poker hands.)
I think it would be better forcing the function to be an equivalence relation using dependent types. ;-) In the absence of dependent types, I think that noone should ever call groupBy with a relation which is not an equivalence. So for me, it really doesn’t matter what the function does if the precondition for calling it is not fulfilled.
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Best wishes, Wolfgang